More and more vehicles are tending to be equipped with retractable headlamps, which the driver only deploys at night, or with retractable windshield wipers which are only deployed when it is raining. When not in use, these members are parked within closed housings which are concealed in the bodywork of the vehicle. By appropriate action on a control switching circuit inside the vehicle, the driver obtains either automatic parking or automatic deployment of the retractable member.
The facility for retraction of such members has a number of advantages, among which may for example be cited an improvement in the aerodynamic characteristics of the vehicle, a reduction in the risk of the members concerned being damaged (for example when the vehicle is passing through an automatic washing machine), and aesthetic improvement generally.
However, retraction of a functional member, for example a windshield wiper, is not a simple operation. In addition, not only is the mechanical construction of retractable members somewhat complex, but their electronic control is also a delicate matter.
Retraction of the windshield wiper blade and of its blade carrier into a housing which is arranged under the hood of the vehicle, in front of the front windshield of the vehicle, necessitates complex successive operations, which comprise:
stopping the sweeping movement of the wiper if wiping is in progress, and return of the blade carrier to a stationary position (commonly referred to, and referred to herein, as its "terminal position");
opening a cover which normally closes the housing, the latter being situated below the hood;
folding the wiper blade along the support arm for the wiper blade carrier, so as to reduce the length of the assembly of the blade and arm to a value which is small enough to enable it to be retracted;
displacing the assembly comprising the wiper blade, the wiper arm and a carrier plate which supports it, into the housing itself under the action of a retracting motor;
and finally, closing the cover so as to totally enclose the wiper within its housing.
Substantially the same operations must also be carried out in the opposite sense for deploying the retractable member from its retracted or parked position. It follows that both retraction and deployment occupy a not insignificant time.
Now, it may happen that the driver of the vehicle may give a command for retraction or deployment of the retractable member, and then immediately afterwards change his mind and so give an order countermanding the previous one. It is highly desirable that the countermanding order should immediately be acted on, so that the driver will obtain the state which he wants (i.e. parked or deployed) as quickly as possible.
In the systems that have been proposed up to the present time, either the countermanding order is carried out only after the system has fully completed its operating sequence in obedience to the first command (in which case the driver's waiting time is maximised), or else the countermanding order is executed at the instant at which the retractable member reaches the end of one of the operating steps which positively define its general sequence of operation. Examples of such substantive operating steps are those listed in the sequence of operation described above.
The above follows, in general, from the fact that the whole sequence of parking and deployment is carried out under the control of a microprocessor or a wired logic system, arranged to draw its data as to the state of the system from sensors which consist of end stop contacts or microswitches arranged in the path of the different moveable members of the system. It is only when a moveable member reaches the end of its movement that the microprocessor knows exactly at what stage of retraction or deployment the system then stands; it thinks that this is the end of a main sequence and that a reverse sequence may be commenced at this stage without any trouble.